Dipyridamole dilates large coronary arteries in conscious dogs

The effects of 0.25 mg/kg dipyridamole on left ventricular (LV) pressures, LV dP/dt, heart rate, aortic pressures, left circumflex coronary blood flow, and left circumflex coronary arterial diameters and on calculations of late diastolic coronary resistance and large coronary cross-sectional area were studied in 15 conscious dogs. Injection of dipyridamole, a drug that has a mechanism of action dependent on myocardial adenosine production, caused sustained increases in mean coronary blood flow (244 +/- 28%), large coronary arterial cross-sectional area (28 +/- 3.2%), heart rate (32 +/- 3.6%), and LV dP/dt (23 +/- 3.0%) and reductions in late diastolic coronary resistance (73 +/- 2.4%) and mean arterial pressure (14 +/- 1.9%). Neither beta-adrenergic-receptor blockade alone nor in conjunction with constant heart rate affected the dilation of large coronary arteries to dipyridamole significantly. Ganglionic blockade with hexamethonium also had little effect on the response of large and small coronary vessels to dipyridamole. Surprisingly neither beta-adrenergic-receptor nor ganglionic blockade abolished the rise in LV dP/dt observed after dipyridamole. Aminophylline, however, effectively eliminated the dilation of large coronary arteries and resistance coronary vessels in response to dipyridamole. In summary, as long as dipyridamole does not induce severe sustained hypotension it exerts potent effects on both coronary arterial resistance and large coronary arteries in the conscious dog. The coronary dilation is independent of reflex adrenergic activation, but appears dependent on myocardial adenosine production.